The present invention relates to a linear actuator comprising an outer section having a longitudinal axis and an inner structure which is fitted inside the outer section and is movable with respect thereto in the direction of said longitudinal axis.
An actuator of this type is generally known in the prior art. Pneumatic and hydraulic cylinders are used for moving all kinds of components which are movable with respect to one another. Motor-driven structures are also known.
There is a need, for furniture, such as chairs, desks and other applications, for an actuator which in the smallest position has a small structural height, with which there is no play between the inner structure and the outer section in any of the extended positions, which is simple and inexpensive to produce and including an autonomous drive.
This aim is realised with an actuator as described above in that the outer section is provided with at least two racks which extend in the direction of said longitudinal axis and the inner structure comprises an equal number of pinions engaging on the racks, said pinions being mechanically linked and at least one pinion being drivable by a motor mounted in said inner structure in order to achieve operation of said actuator.
The invention is based on the insight of providing the inner structure with an (electric) drive motor. This motor drives at least one pinion. Further pinions are fitted in order to provide accurate guiding of the inner section with respect to the outer section. If, in accordance with an advantageous embodiment of the invention, both the outer section and the inner structure are constructed as square tubular sections, it is advantageous that two drive pinions are provided which are mounted close to the mid-points of two opposing sides, as well as two auxiliary pinions which take up play and which are likewise mounted opposite one another on the two mid-points of the two adjoining sides. In such a case the first-mentioned and the last-mentioned pinions are coupled to one another by a connecting shaft. It has been found that in this way a particularly small space requirement coupled with an appreciable stroke can be obtained with a compact motor. It has also been found that negligible play between the inner structure and the outer section occurs throughout said stroke and a particularly rigid unit is produced.
It is possible for two pinions/racks to suffice. However, according to an advantageous embodiment of the invention at least three racks and an equal number of pinions are provided, at least two of said pinions being mechanically coupled.
Retaining means which provide for positioning of the inner structure and the outer section with respect to one another can be provided as additional elements to take up possible play. This retaining means can, for example, be arranged to provide fixed engagement between the non-driven pinions and the rack concerned. Furthermore, it is possible to choose the thickness of the racks such that the inner structure is held in position with respect to the outer section.
Although it has been described above that both the outer section and the inner structure are constructed as square tubular sections, it must be understood that any other shape imaginable in the prior art is possible. Such a shape varies from triangular to polygonal and from circular to elliptical, it not being necessary for the outer section to have a shape which is congruent with the shape of the inner structure. The motor described above can be any motor known from the prior art, but an electric motor that drives the pinions concerned, with or without the aid of a transmission, is preferred. By this means it is possible to provide a very compact structure, with which appreciable loads can be moved, with a small space requirement. An actuator of this type can, for example, be used for the column of a chair or also for adjusting desks. It must be understood that this is merely an example and that many other applications of the actuator according to the present invention are conceivable.